There are known control devices with limit switches referred to as “Limit Switch Boxes” used to control the position of valves and actuators. These devices comprise an electric circuit on which one or more limit switches are mounted, as well as a driving assembly comprising a shaft connectable to a valve or to an actuator through a suitable coupling. The driving assembly further comprises one or more cams keyed on the shaft and configured to interact with the respective limit switches so as to enable or inhibit operation of the valve or actuator.
Switches having a push button may be directly controlled by the cams, whereas limit switches in the form of proximity sensors may be controlled indirectly by way of a ferromagnetic material element or a magnet associated with the cams.
The driving assembly and the electrical circuit are generally accommodated in a container that protects them from atmospheric agents and which may be optionally configured to resist fire and/or explosion. The container is typically provided with a plurality of openings configured to allow passage of electric cables and an visual position indicator associated with the shaft. This allows operators to quickly obtain information about the position of a valve or actuator, corresponding to what is detected by the limit switches.
The driving assemblies employed in control devices with limit switches are standardized components provided with means for adjusting the angular position of the cams, which allows to arrange them according to the position of the respective switches and/or proximity sensors mounted on the electric circuit of a specific device.
Known control devices with limit switches comprise shafts on which one or more annular elements are keyed on whose peripheral walls a plurality of alternating lands and grooves are formed in a longitudinal direction that together define a ribbed surface. On these surfaces it is possible to engage respective cams by way of a shape coupling. For this purpose the surface of the mounting hole of each cam comprises a plurality of longitudinal lands and grooves whose shape corresponds to the shape of the lands and grooves of the ribbed surface of the annular elements.
The cams are axially movable relative to the respective annular elements between a locking position, wherein the ribbed surfaces are coupled with each other, and an unlocking position, wherein the ribbed surfaces are disengaged and each cam may freely rotate about the shaft, whose cross section has a diameter smaller than the diameter of the annular elements.
By temporarily removing the shape coupling between cams and shaft, it is thus possible to change their relative position, which allows to configure the driving assembly they form so as to allow to assemble it in a control device provided with a specific electrical circuit with limit switches.
In order to allow maintenance of the relative position between the annular elements and the respective cams in the locked position, the cams are urged into this position by coil springs suitably keyed on the shaft and axially restrained thereto. The axial movement of each cam along the shaft is limited by abutment surfaces formed at one end of the mounting hole opposite to the end facing the respective annular element.
The publication U.S. Pat. No. 5,298,700 A discloses a module for limit switch boxes. The module comprises a shaft that may be rotatably coupled to a valve or an actuator and one or more cams keyed on the shaft and configured to drive limit switches. The shaft comprises a gripping surface and each cam comprises a radial clamping mechanism whose gripping members are arranged at a respective through hole configured to allow to assemble the cam on the shaft.